June 2010

Biomechanics may offer clues

Too often, by the time Charcot neuroarthropathy is diagnosed, it is too late to do much more than accommodate the resulting deformity. That’s why researchers from Germany and the U.K. are working to find ways of screening for patients at risk for Charcot, which would facilitate earlier and more effective intervention.

The search is made more complicated by the increasingly accepted idea that two different pathologic pathways, neurovascular and neuro-traumatic, likely contribute to Charcot neuroarthropathy individually or in combination.

“The challenge lies in gathering supportive evidence in how we assess the biomechanics of the foot,” said William Munro, MBAPO, a clinical associate at the University of Strathclyde in Glasgow, Scotland, in a presentation at the ISPO meeting in Leipzig.

A German study presented at the same meeting offers a preliminary look at this type of supportive evidence. Researchers from the University of Applied Sciences in Munster analyzed seven patients with unilateral Charcot foot localized to the metatarsal area (Sanders pattern II or III) and no pathological findings on the contralateral foot, along with five control subjects who did not have diabetes. Motion analysis and pressure measurement were used to assess the subjects as they walked along a nine-meter walkway.

The investigators found that the patients with Charcot demonstrated a greater drop in medial longitudinal arch angle and more limited range of motion at the first metatarsophalangeal joint compared to the control subjects, even on the asymptomatic side.

“The atrophic muscles of the patients cannot impede the os navicular drop, which results in higher joint pressure. Higher forces, body weight and momentum damage the passive structure and cause injury,” said Holger Burgwal, a researcher from the university, who presented the findings at the ISPO meeting. “This collapse of the arch is striking and strange since it also happens on the foot without Charcot.”

The results suggest that practitioners should look for limited mobility at the first MTP joint, particularly limited extension, as a potential risk factor for Charcot neuroarthropathy, Burgwal said. Preventive support of the medial longitudinal arch with insoles is indicated, he said, but noted that practitioners should be careful that the arch support provided by the insole doesn’t inadvertently increase pressure on the MLA.

“I would always measure the pressure to exclude that risk,” he said.

Practitioners should also be aware that some diabetic footwear may actually limit the mobility of the first MTP joint, which underscores the importance of proper shoe fitting in the at-risk patient population, Burgwal said.

Munro, who is working with researchers from Kings College in London to explore both neuro-traumatic and neurovascular causes of Charcot, also believes that biomechanical assessment can be a key to early intervention. Even something as universal as pronation, for example, creates an imbalance between the medial and lateral forefoot that could trigger a neuro-traumatic cascade.

“Think of pronation as a low-grade repetitive strain,” he said.

From a neurovascular perspective, the Kings College group and others are studying how proinflammatory cytokines contribute to Charcot neuroarthropathy and how those effects differ for type 1 and type 2 diabetes.

Ultimately, Munro said, the goal is to catch the arthropathy while it is still in the acute inflammation or pre-fragmentation phase (Eichenholtz stage 0).

“Pre-fragmentation to me is what we should be working toward,” Munro said. “If we can get the patient at this stage, we think we can switch the process off. Certainly with chronic Charcot we’ve missed the boat, so it’s very important to get to it at the pre-fragmentation stage.”

German practitioners may be a little late to the party when it comes to total contact casting, but their results compare favorably to previously published outcomes – a sign that geography and language are not impediments to the treatment’s repeatability.

Researchers from the Diabetes Center of Mergentheim in Mergentheim, Germany, conducted a multi-center study of TCC effectiveness in 50 patients from six foot treatment facilities certified by the German Diabetes Association. Patients were treated with moist wound management and pressure relief using a bivalved, fiberglass TCC. The TCC was fitted by a wound care specialist, orthopedic shoemaker, diabetologist, or orthopedic ward personnel. All patients were treated on an outpatient basis.

TCC was discontinued in four patients, one who developed a lesion following amputation of the big toe, one who experienced leg pain, and two for reasons related to compliance. In the remaining 46 patients, healing time averaged 37 days and ranged from 7 days to 157 days.

The findings, presented at the ISPO meeting in Leipzig, are similar to those of previous studies. In a 1984 study in the Archives of Physical Medicine & Rehabilitation, researchers from the University of Texas Health Science Center found that TCC healing time averaged 38.3 days in 16 of 22 patients. In a 1998 study in the Journal of Rehabilitation Research & Development, researchers from the same institution found that the treatment was associated with a mean healing time of 38.8 days.